The present invention generally relates to a method and apparatus for adhering flowable solder to a solder-wettable substrate together with limiting the spreading of molten solder over the surface of the substrate, without the aid of a protective coating adhered to the substrate, and without the aid of a barrier between the substrate and the atmosphere. The present invention generally relates to a solder-wettable substrate in the form of an electrical terminal having a flow deposited quantity of solder adhered to a selected portion of the terminal with the solder being confined to the selected portion without the aid of a protective coating on the terminal or a barrier between the terminal and the atmosphere. The present invention relates to an electrical terminal having a plated aperture provided in a board substrate with a quantity of solder flowably adhered to a selected portion of the terminal, with the solder being reflowed and wicking into the clearance between the substrate aperture and the inserted terminal, such wicking action preventing escape of the reflowed solder and causing the formation of solder fillets surrounding the terminal at the substrate surface. The present invention further relates generally to a method of treating an electrical contact having a band of solder adhered thereto, and more particularly to a method of applying pressure to a contact having a band of solder adhered thereto. In addition, the present invention relates to a unique solder stripped contact structure having a flattened solder band adhered thereto.
Heretofore, flowably adhering solder to a selected portion of a solder-wettable substrate required the use of a high temperature resistant and solder resistant material adhered to the substrate and defining a structural barrier adjacent to the selected portion on which the solder was to be adhered. The resistant material also formed a barrier between the substrate surface and the atmosphere. According to the present invention, solder may be flow deposited to a selected portion of a solder-wettable substrate without the need for the intimate contact heretofore required between a solder stop-off and the substrate to be coated with the solder. Another equally important objective of the present invention allows a substrate to be provided with a flowably deposited layer of solder material adhered to selected surfaces of the terminal, with the solder layer desirably terminating at an imaginary barrier line. The imaginary barrier line is created by a purposely formed capillary, with a flux coated surface of the substrate forming one surface of the capillary and a non-wettable solder resisting material forming another opposed surface of the capillary, the presence of the solder resistant material stopping the flow of molten solder over the substrate surface at the imaginary barrier line adjacent to the capillary.
The invention further relates to a method of mounting an electrical terminal in a plated aperture of a board type substrate upon removal of flux residue from the terminal, and upon inserting the terminal together with its adhered layer of solder within the metallized aperture. The solder is then reflowed and the solder is drawn by a wicking action into the clearance between the substrate aperture and the inserted terminals. Sufficient solder is provided to form solder fillets surrounding the terminal at each open end of the substrate aperture.
In addition, the invention relates to a method of modifying the solder striped contacts, produced according to the method described above, whereby their insertion or mounting in the plated apertures of the above-described board type substrate is facilitated. More particularly the solder deposited on the individual contacts according to the above-described method generally forms a band surrounding each contact when it hardens. This solder band is generally of a diameter which is somewhat larger than the diameter of the plated apertures in the board type substrate material. The solder band therefore interfits frictionally with the interiors of the plated apertures, and requires the use of a substantial amount of pressure in forcing the solder striped contacts into the apertures. It is noted that the pressure may be applied either by pressing contacts into the apertures from the top, or preferably, pulling them through the apertures by applying a drawing force to the extended lower portions thereof. Although it is desirable that a friction fit should result upon insertion of the striped contacts into the apertures, it is not desirable that an extremely high pressure or force be required to mount the contacts in the apertures, since large forces may deform or stretch the contacts, or may cause the solder bands to fracture or break partially away from the contacts, thereby reducing the remaining amount of solder adhered to the contacts to a level below that which is required to hold the contacts securely in place upon being reflowed. Accordingly, the present invention includes a technique for applying pressure to both sides of the solder bands adhered to each of the contacts, resulting in two effects. First, the flattened solder bands are smaller in diameter at their flattened portions than the plated apertures, thereby reducing the friction, and correspondingly the force required to insert the solder striped contacts into the plated apertures. Second, in the process of flattening, hairline fractures are created in portions of the solder band, causing these portions to shear away with relative ease as the band comes in contact with the edge portions of the plated apertures. Accordingly, the flattened solder bands reduce the amount of force required to mount the solder striped contacts in the board type substrates, but do not prevent the formation of desirable friction or interference fits, nor do they interfere in any manner with the remaining operational aspects of the solder striped contacts.
It is therefore an object of the present invention to provide an article of manufacture fabricated from a solder wettable material and provide thereon with a flowably deposited layer of solder adhered to selected portions of the article and with the margins of the solder terminating at desired imaginary barrier lines.
Another object of the present invention is to provide a solder stop-off for limiting the spreading of a flowable solder over a solder wettable surface, including a solder non-wettable material adjacent to the solder wettable surface and forming a capillary, with the presence of the nonwettable material repelling the solder and preventing flow of the solder into the capillary.
Yet another object of the present invention is to provide a solder stop-off for limiting the spreading of a flowable solder over a solder wettable surface by the presence of a nonwettable material adjacent to the wettable surface and preventing flow of the solder along the wettable surface adjacent to the surface of the solder nonwettable material.
It is another object of the present invention to provide a solder resistant capillary for limiting the flow of molten solder, with the capillary formed between a solder wettable surface and another solder nonwettable surface.
Still another object of the present invention is to provide a method of mounting an electrical terminal in a plated aperture of a board type substrate wherein the terminal together with a flowably applied layer of solder adhered to selected portions of the terminal is inserted into the substrate and the solder thereof is reflowed, to fill the clearance between the substrate aperture and the inserted terminal, and to form solder fillets surrounding the terminal.
It is yet another object of the present invention to provide a selectively pre-soldered electrical terminal, the terminal including a flow deposited layer of solder adhered to a selected portion of the terminal with solder spreading limited by the presence of a solder nonwettable surface adjacent to but not necessarily touching the electrical terminal.
Still another object of the present invention is to provide an article of manufacture fabricated from a solder wettable material and provided thereover with an adhered layer of flowably deposited solder over the article without the need for a solder resistant material coating the article or a barrier between the article and the atmosphere.
Another object of the present invention is to provide method and apparatus for flow depositing adhered layers of solder in controlled band widths to respective solder wettable articles of manufacture serially in an automated operation without the need for a solder resistant coating on the articles or a barrier between the articles and the atmosphere.
Yet another object of the present invention is the provision of a novel method for treating solder striped contacts prior to their insert into a board type substrate.
A still further object of the present invention is the provision of a novel contact structure having a flattened solder band adhered thereto.
Another object of the present invention is the provision of a unique method for flattening solder bands adhered to contact structures.
Briefly, these and other objects of the invention are achieved by providing an electrical terminal with a localized quantity of solder applied by flow deposition techniques. The solder is limited from spreading over the surface of the electrical terminal by the presence of a solder-non-wettable material positioned adjacent to, but not touching the electrical terminal. This application technique provides a solder stop-off without a need for a solder resistant coating or an atmospheric barrier which is adherent to the electrical terminal and which must subsequently be physically removed. The terminals thus treated have bands of solder adhered to them, and are adapted to be inserted into plated-through apertures in a board or substrate material. The solder bands are then reflowed, and the resulting molten solder is drawn by a wicking action into the apertures in the substrate to firmly hold the electrical terminals in place. A method and apparatus are also disclosed for flattening the solder bands to facilitate the insertion of the terminals into the plated-through apertures. Pressure is applied to the solder bands, causing them to be flattened and causing a plurality of hairline fractures to be created within the flattened bands. The flattened bands reduce the insertion resistance by reducing the area of interference between the flattened bands and the edges of the apertures. In addition, the hairline fractures substantially weaken the structural integrity of the solder bands, permitting the solder to be readily folded back or scraped away from the terminals as the terminals are forcibly inserted into appropriate apertures whose diameters are smaller than the widths of the flattened solder bands.